DESCRIPTION (Investigator's Abstract): Many procedures in experimental neuroscience depend upon accurate and precise surgical access to specific structures in the brain, in reference to known landmarks on the skull and three-dimensional information about brain structures as published in stereotaxic atlases. The current stereotaxic instrument has seen little change from the date of its original design, about 35 years ago. In the meantime, the machine tool industry has seen dramatic advances in the accuracy and precision of basic mechanical mechanisms. The purpose of this project is to determine the accuracy and precision that might be obtained with a stereotaxic instrument that has been completely re-designed using modern machine tool principles. This new design includes a precision surface plate which provides a reliable planar datum. Second, a new universal manipulator will be developed using precision linear scales and digital readouts with a resolution of 1 micron. Finally, an automatic indexing tool holder will allow the user to interchange centering scopes, drills, and electrode holders on a common vertical axis. This instrument is expected to improve the accuracy of stereotaxic surgery by a factor of 5- to 20-fold; these results will be verified by an independent calibration laboratory accredited by the NIST.